Estudio fenomenológico de extensiones del sector escalar del modelo estándar

En esta tesis se abordan distintos estudios fenomenológicos de posibles extensiones en el sector escalar del Modelo Estándar de partículas y sus interacciones (SM). En el primero de los estudios realizados, el SM se extiende a partir de la inclusión de una interacción de tipo pseudoescalar entre el bosón de Higgs y el quark top, y la modificación de la intensidad del acoplamiento escalar usual. La presencia del nuevo acoplamiento y, en particular, la determinación del signo relativo entre los acoplamientos escalar y pseudoescalar se examinan a partir de la construcción y posterior análisis de sensibilidad de una colección de observables impares ante CP. El estudio llevado a cabo no solo permite recuperar los observables definidos en la literatura sino que también da lugar a observables superadores cuya importancia podría evidenciarse a corto plazo en el LHC. El segundo de los estudios extiende el contenido de partículas del SM introduciendo un triplete electrodébil escalar de leptoquarks, lo cual da lugar a nuevas interacciones leptón-quark. El impacto de este modelo en el espectro de neutrinos de ultra alta energía observado en IceCube y los límites que dicho espectro impone en los nuevos parámetros son analizados cuidadosamente, con especial interés en el ligero exceso de eventos observado en la región del PeV. Asimismo, se obtienen las restricciones provenientes tanto de búsquedas dedicadas y más generales en el LHC como de observables de física de bajas energías, las cuales se contrastan posteriormente con los resultados derivados en el contexto de IceCube. Por último, en el tercer estudio también se amplía el SM a partir de la introducción de nuevas partículas, más precisamente, suponiendo la presencia de un escalar cargado. Esta extensión es puesta a prueba en el decaimiento específico tau -> K pi pi nu a través de la construcción y análisis de observables pares e impares ante CP. Asimismo, se investiga la utilidad de los observables propuestos para testear el modelo concreto de dos dobletes de Higgs alineados. La sensibilidad del conjunto de observables construidos podría ser explotada en el contexto de las futuras Super fábricas de mesones B.Facultad de Ciencias Exacta

LHC sensitivity to singly charged scalars decaying into electrons and muons

Current LHC searches for nonsupersymmetric singly charged scalars, based on two-Higgs-doublet models, in general, focus the analysis in third-generation fermions in the final state. However, singly charged scalars in alternative extensions of the scalar sector involve Yukawa couplings not proportional to the mass of the fermions. Assuming the scalar decays into electrons and muons, it can manifest cleaner experimental signatures. In this paper, we suggest that a singly charged scalar singlet, with electroweak production, can start to be probed in the near future with dedicated search strategies. Depending on the strength of the Yukawa couplings, two independent scenarios are considered: direct pair production (small couplings) and single production via a virtual neutrino exchange (large couplings). We show that, up to a mass as large as 500 GeV, most of the parameter space could be excluded at the 95% C.L. in a high-luminosity phase of the LHC. Our results also apply to other frameworks, provided the singly charged scalar exhibits similar production patterns and dominant decay modes.Instituto de Física La Plat

Implications of a electroweak triplet scalar leptoquark on the ultra-high energy neutrino events at IceCube

We study the production of scalar leptoquarks at IceCube, in particular, a particle transforming as a triplet under the weak interaction. The existence of electroweak-triplet scalars is highly motivated by models of grand unification and also within radiative seesaw models for neutrino mass generation. In our framework, we extend the Standard Model by a single colored electroweak-triplet scalar leptoquark and analyze its implications on the excess of ultra-high energy neutrino events observed by the IceCube collaboration. We consider only couplings between the leptoquark to first generation of quarks and first and second generations of leptons, and carry out a statistical analysis to determine the parameters that best describe the IceCube data as well as set 95% CL upper bounds. We analyze whether this study is still consistent with most up-to-date LHC data and various low energy observables.Facultad de Ciencias ExactasInstituto de Física La Plat

Potential discovery of staus through heavy Higgs boson decays at the LHC

In this work we present a new search strategy for the discovery of staus at the LHC in the context of the minimal supersymmetric standard model. The search profits from the large s-channel b-quark annihilation production of the heavy CP-even and CP-odd Higgs bosons (H/A) which can be attained in regions of tan β ≫ 1 that avoid the stringent H/A → τ⁺ τ⁻ searches via decays into stau pairs. We also focus on regions where the staus branching ratios are dominated by the decays into a tau lepton and the lightest neutralino. Thus the experimental signature consists of final states made up of a tau-lepton pair plus large missing transverse energy. We take advantage of the large stau-pair production cross sections via heavy Higgs boson decays, which are between one or two orders of magnitude larger than the usual electroweak production cross sections for staus. A set of basic cuts allow us to obtain significances of the signal over the SM backgrounds at the discovery level (5 standard deviations) in the next LHC run with a center-of-mass energy of 14 TeV and a total integrated luminosity of only 100 fb-1.Facultad de Ciencias ExactasInstituto de Física La Plat

Constraining R-axion models through dijet searches at the LHC

The search at hadron colliders for new massive resonances of a few 100 GeVs that couple effectively to colored states is an extremely challenging issue, due principally to the presence of large QCD multijet backgrounds at this energy, rendering the searches at the LHC particularly difficult. Recently, it was realized that these large backgrounds could be overcome by demanding one high-pT jet from initial-state radiation (ISR) and by means of novel jet-reconstruction techniques through which the resulting hadronized products of the massive resonances are reconstructed as a fat-jet, a unique large-radius jet. The ATLAS and CMS Collaborations have recently reported searches for the experimental signature of a single fat-jet in association with an ISR jet. Models of dynamical supersymmetry breaking with an spontaneously broken R-symmetry give rise to the appearance of a pseudo-Nambu?Goldstone boson called the R-axion, which naturally tends to be light. In the parameter space regions where the anomalous R-axion coupling to gluons is boosted, these models can be tested against these new LHC dijet searches. Taking into account the CMS search, we apply the qμ statistical method to the signal events against the background-only expectation and obtain the 95% C.L. exclusion limits on the most relevant model parameters for a particular messenger sector, namely, the R-axion mass ma, the decay constant fa, and the number of color messengers N, being these limits suitable to be applied to more general models with axion-like particles.Fil: Arganda Carreras, Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Autónoma de Madrid; EspañaFil: Medina, Anibal Damian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Mileo, Nicolás Ismael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Morales, Roberto Anibal. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Szynkman, Alejandro Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Implications of a electroweak triplet scalar leptoquark on the ultra-high energy neutrino events at IceCube

We study the production of scalar leptoquarks at IceCube, in particular, a particle transforming as a triplet under the weak interaction. The existence of electroweak-triplet scalars is highly motivated by models of grand unification and also within radiative seesaw models for neutrino mass generation. In our framework, we extend the Standard Model by a single colored electroweak-triplet scalar leptoquark and analyze its implications on the excess of ultra-high energy neutrino events observed by the IceCube collaboration. We consider only couplings between the leptoquark to first generation of quarks and first and second generations of leptons, and carry out a statistical analysis to determine the parameters that best describe the IceCube data as well as set 95% CL upper bounds. We analyze whether this study is still consistent with most up-to-date LHC data and various low energy observables.Facultad de Ciencias ExactasInstituto de Física La Plat

Search strategies for pair production of heavy Higgs bosons decaying invisibly at the LHC

The search for heavy Higgs bosons at the LHC represents an intense experimental program, carried out by the ATLAS and CMS collaborations, which includes the hunt for invisible Higgs decays and dark matter candidates. No significant deviations from the SM backgrounds have been observed in any of these searches, imposing significant constraints on the parameter space of different new physics models with an extended Higgs sector. Here we discuss an alternative search strategy for heavy Higgs bosons decaying invisibly at the LHC, focusing on the pair production of a heavy scalar H together with a pseudoscalar A, through the production mode qq¯→Z⁎→HA. We identify as the most promising signal the final state made up of 4b+ET miss, coming from the heavy scalar decay mode H→hh→bb¯bb¯ with h being the discovered SM-like Higgs boson with mh=125GeV, together with the invisible channel of the pseudoscalar. We work within the context of simplified MSSM scenarios that contain quite heavy sfermions of most types with O(10)TeV masses, while the stops are heavy enough to reproduce the 125 GeV mass for the lightest SM-like Higgs boson. By contrast, the gauginos/higgsinos and the heavy MSSM Higgs bosons have masses near the EW scale. Our search strategies, for a LHC center-of-mass energy of s=14TeV, allow us to obtain statistical significances of the signal over the SM backgrounds with values up to ∼1.6σ and ∼3σ for total integrated luminosities of 300fb−1 and 1000fb−1, respectively.Fil: Arganda, E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Diaz-Cruz, J.L.. Benemérita Universidad Autónoma de Puebla; MéxicoFil: Mileo, N.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Morales, R.A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Szynkman, A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Search strategies for pair production of heavy Higgs bosons decaying invisibly at the LHC

The search for heavy Higgs bosons at the LHC represents an intense experimental program, carried out by the ATLAS and CMS collaborations, which includes the hunt for invisible Higgs decays and dark matter candidates. No significant deviations from the SM backgrounds have been observed in any of these searches, imposing significant constraints on the parameter space of different new physics models with an extended Higgs sector. Here we discuss an alternative search strategy for heavy Higgs bosons decaying invisibly at the LHC, focusing on the pair production of a heavy scalar H together with a pseudoscalar A, through the production mode qq¯→Z*→HA. We identify as the most promising signal the final state made up of 4b+EmissT, coming from the heavy scalar decay mode H→hh→bb¯bb¯ with h being the discovered SM-like Higgs boson with mh=125GeV, together with the invisible channel of the pseudoscalar. We work within the context of simplified MSSM scenarios that contain quite heavy sfermions of most types with O(10)TeV masses, while the stops are heavy enough to reproduce the 125 GeV mass for the lightest SM-like Higgs boson. By contrast, the gauginos/higgsinos and the heavy MSSM Higgs bosons have masses near the EW scale. Our search strategies, for a LHC center-of-mass energy of √s=14TeV, allow us to obtain statistical significances of the signal over the SM backgrounds with values up to ∼1.6σ and ∼3σ for total integrated luminosities of 300fb−1 and 1000fb−1, respectively.Facultad de Ciencias ExactasInstituto de Física La Plat

Search strategies for pair production of heavy Higgs bosons decaying invisibly at the LHC

The search for heavy Higgs bosons at the LHC represents an intense experimental program, carried out by the ATLAS and CMS collaborations, which includes the hunt for invisible Higgs decays and dark matter candidates. No significant deviations from the SM backgrounds have been observed in any of these searches, imposing significant constraints on the parameter space of different new physics models with an extended Higgs sector. Here we discuss an alternative search strategy for heavy Higgs bosons decaying invisibly at the LHC, focusing on the pair production of a heavy scalar H together with a pseudoscalar A, through the production mode qq¯→Z*→HA. We identify as the most promising signal the final state made up of 4b+EmissT, coming from the heavy scalar decay mode H→hh→bb¯bb¯ with h being the discovered SM-like Higgs boson with mh=125GeV, together with the invisible channel of the pseudoscalar. We work within the context of simplified MSSM scenarios that contain quite heavy sfermions of most types with O(10)TeV masses, while the stops are heavy enough to reproduce the 125 GeV mass for the lightest SM-like Higgs boson. By contrast, the gauginos/higgsinos and the heavy MSSM Higgs bosons have masses near the EW scale. Our search strategies, for a LHC center-of-mass energy of √s=14TeV, allow us to obtain statistical significances of the signal over the SM backgrounds with values up to ∼1.6σ and ∼3σ for total integrated luminosities of 300fb−1 and 1000fb−1, respectively.Facultad de Ciencias ExactasInstituto de Física La Plat

Pseudoscalar top-Higgs coupling: exploration of CP-odd observables to resolve the sign ambiguity

We present a collection of CP-odd observables for the process pp→t(→bℓ+νℓ)t¯(→b¯ℓ−ν¯ℓ) H that are linearly dependent on the scalar (kt) and pseudoscalar (k˜t) top-Higgs coupling and hence sensitive to the corresponding relative sign. The proposed observables are based on triple product (TP) correlations that we extract from the expression for the differential cross section in terms of the spin vectors of the top and antitop quarks. In order to explore other possibilities, we progressively modify these TPs, first by combining them, and then by replacing the spin vectors by the lepton momenta or the t and t¯ momenta by their visible parts. We generate Monte Carlo data sets for several benchmark scenarios, including the Standard Model (kt = 1, k˜t= 0) and two scenarios with mixed CP properties (kt = 1, k˜t = ± 1). Assuming an integrated luminosity that is consistent with that envisioned for the High Luminosity Large Hadron Collider, using Monte Carlo-truth and taking into account only statistical uncertainties, we find that the most promising observable can disentangle the “CP-mixed” scenarios with an effective separation of ∼ 19σ. In the case of observables that do not require the reconstruction of the t and t¯ momenta, the power of discrimination is up to ∼ 13σ for the same number of events. We also show that the most promising observables can still disentangle the CP-mixed scenarios when the number of events is reduced to values consistent with expectations for the Large Hadron Collider in the near term.Facultad de Ciencias ExactasInstituto de Física La Plat